Meteorologists recommend new standards for red flag wildfire warnings

Meteorologists recommend new standards for red flag wildfire warnings

Strong winds blow snow near a burned-out car that was left on top of a hill during the Marshall Fire in Superior on January 4, 2022.

Meteorologists did not issue a red flag warning for wildfire danger ahead of the deadly wind-driven Marshall Fire in 2021 because humidity levels were not low enough to trigger such an alert.

However, NOAA scientists working in Boulder are now recommending relaxing the humidity threshold and changing the red flag warning criteria to account for the potential overall rate of wildfire spread.

They also recommend using the Federal Emergency Management Agency's alert system to warn people in fire zones of the dangers.

These recommendations were included in a new report published last month in the journal Weather and Forecasting, a publication of the American Meteorological Society. The team presented its findings on Tuesday to other scientists, emergency management specialists and the media.

The storm that sent flames across part of Boulder County on December 30, 2021, was unique, with hurricane-force winds blowing nonstop for 11 hours, researchers said. Those strong, persistent winds were the main reason the fire spread the way it did, said Stan Benjamin, lead author of the report and a scientist at the Cooperative Environmental Science Research Institute at the University of Colorado Boulder.

“Even without the fire, the winds that day would have been a big story,” said Eric James, a scientist at NOAA's Global Systems Laboratory in Boulder and one of the report's authors.

However, high wind days like Dec. 30, 2021, are becoming less frequent and less severe in Boulder County, according to historical weather data.

Since 1996, wind gust records have become more accurate, so scientists studied that data to see how many days wind speeds exceeded 70 knots, or 80.5 mph, in Boulder, Larimer and northern Jefferson counties.

Paul Schlatter, science and operations officer for the National Weather Service in Boulder, said data shows there are now two fewer days a year where wind speeds exceed 70 knots than there were in 1996. As for days when wind speeds exceed 90 knots, or 103.5 mph, they now occur only once every five years compared to the first 10 years of data, when 100 mph winds occurred on average two days a year.

Scientists are working to explain why there are so few strong wind days.

An investigation by the Boulder County Sheriff's Office and District Attorney's offices concluded that the Marshall Fire had two points of origin: embers from a weeklong fire on property owned by the Twelve Tribes religious cult and an Xcel Energy power line that became loose and caused an electrical arc.

Those locations were about 2,000 feet away, near the intersection of Colorado 72 and Colorado 93, one of the windiest spots in Boulder County, Schlatter said.

“We knew it was going to be bad.” He said. “Never start a fire there — that's what we got. We had two fires there.”

Meteorologists with the National Weather Service issued a high wind warning at 3 a.m. on the day of the fire and began posting it on social media at 4 a.m., he said. About 400 other agencies are notified when the weather service is in a state of severe weather.

In Boulder County, high wind notices are sent when wind speeds are expected to reach 75 mph or higher. In most parts of the United States, these warnings are issued when wind speeds exceed 58 mph.

“It's a windy place out here and we would issue high wind warnings all the time if we had a lower threshold,” Schlatter said.

But the humidity that day didn't drop below 20%, meaning it wasn't low enough to trigger the weather service to issue a red flag warning. These warnings are issued when there is an increased risk of fire hazard due to low humidity, high temperatures and strong winds.

The scientists recommended changing the humidity standard, although they did not make a specific recommendation on a new threshold or whether it should be eliminated entirely.

Red Flag Guidelines were written decades ago and were intended to provide advice to fire departments, forestry workers and others whose jobs centered around fire prevention. But over the years, Schlatter said, it has become a common tool.

The Marshall Fire is the most destructive in Colorado, destroying more than $2 billion worth of property in Superior, Louisville and unincorporated Boulder County. Two people died in the fire, and scientists said Tuesday that the low number was astonishing given how quickly the fire spread and how chaotic the public evacuation notices were.

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *